/Engine/Plugins/Experimental/MeshModelingToolsetExp/Source/MeshModelingToolsExp/Public/MeshSelectionTool.h
Expand the selection to include all triangles with Materials matching the Materials on the currently selected triangles
[UFUNCTION](Programming/UnrealArchitecture/Reference/Functions)(CallInEditor, Category=SelectionEdits, Meta=(DisplayPriority=9)) void ExpandToMaterials()